Jump to content
SAU Community

Recommended Posts

Hi. I have a built RB25. Since I got the car a year ago, it's had this annoying knocking sound. Does not sound like it's any different depending on engine temp.

I don't think the sound has gotten much worse. Been two times for mapping in dyno, one drag race and 13000km on the road just last summer. Now after using the car for a few days the oil starts to get a strong smell of fuel. Injectors is tested and cleaned. Nothing wrong with them. Does not look like the engine has any noticable blow by either.

Engine is bored, CP Pistons (87mm), Eagle rods. All bearings are ACL Race series. Compression test was: 9.9, 9.9, 10, 10, 10, 10.5

Anyone had the same sound from their's RB? Listened with a stethoscope and knocking is most noticeable from sylinder 6 on block- intake side. 

 

Edited by KimHaugli
Link to comment
https://www.sau.com.au/forums/topic/480630-built-rb25-piston-slap/
Share on other sites

Your compressions are quite low but I'm guessing it was built that way.  The noise sounds a bit of a worry .  Were you able to  narrow down the source to high up (valve gear) or lower down in the block?  Is your VCT working OK?

8 hours ago, KiwiRS4T said:

Your compressions are quite low but I'm guessing it was built that way.  The noise sounds a bit of a worry .  Were you able to  narrow down the source to high up (valve gear) or lower down in the block?  Is your VCT working OK?

Sound was faint in the head and a lot more noticeable on the block. VCT should be fine. I guess the sound would come from the front if that was the problem?

Yeah, so, the obvious suspects for block noise are piston slap, gudgeons and rod bearings. Bit hard to say which it might be from here though.

The video from inside the car sounds more like a spun bearing than piston slap. Hard to believe that it has been making that noise for 13000km without either it exploding (if it was a bearing) or you taking it apart to find out what the hell is wrong. There's no way that I would drive it if it sounded like that.

The video from inside the engine bay sounds so much more like a stuck/collapsed lifter than anything from lower down. There's no way that I would drive it if it sounded like that.

All lifters has been opened and cleaned out before I started using the car again this year. Many were saying lifters last year but they looked perfect. 

Last year when I started to get fuel in the oil is when I parked the car. Got the map checked and it was way too rich. Assembled the head, got off to dyno. Noise was still there and 3 days after, strong smell of fuel in oil. 

On 20/06/2020 at 2:10 AM, GTSBoy said:

That just sounds like lifters too.

TAKE IT APART!

Or at least take it to a decent mechanic.

I find it weird for it to be the lifters as everyone told me it was last year. Took them out this winter and they have been opened and cleaned out. Still the same sound, and no one looked like beeing broken. 

After using the car a little the last weeks the sound is getting worse when the engine is cold, and is more noticeable now when warm. So the engine is coming out ?

This actually is a really interesting post... to start, a small amount of  Piston slap Is actual a normal occurrence in forged builds under certain conditions believe it or not.

1# Forged pistons are honed/bored at slightly higher than stock piston to wall clearance over factory cast pistons 

2# Forged pistons and cast pistons dont have the same expansion under heat, forged pistons expand more hence and take more time too and thats why they need a greater tolerance. Sometimes depending on the application... forged pistons when in the bores can even rock back and forth to the point where they go “click clack” when moving them by hand. Crazy to think about but look it up on youtube from HPacademy. 

#3 Forged pistons usually have a central gudgeon pin location, where as cast/stock are made with an offset pin location on all OEM pistons, which helps reduce noise.

Now, from my experience with my forged rb25neo, i do have some very slight slap on cold start but within 5-10 mins it is 100% Gone. This is considered normal with forged motors

In your case with ur engine warmed up still slapping loud like hell and with ur compression readings, it may be that ur clearances are completely off and this is 100% the machinist/engine builders fault for not doing it or checking it correctly. 
 

Sorry to hear about it but keep us updated, very curious to know what happened or if its something else entirely.

5 hours ago, Dil-Dog said:

But keep us updated, very curious to know what happened or if its something else entirely.

Yeah, I will come with updates when I get it out.

I guess there will be scarring on the side of pistons or cylinders if the engine has piston slap and been driven that far with it? When I had the head off I could not see any damage to the cylinder walls, but you never know what hides lower in the cylinder when piston is in.

1 hour ago, Dil-Dog said:

Yeah man, good luck and take pics and get back to us 

Just got it confirmed 30 minutes ago. Piston slap ? but the mechanic said that the sound was not that bad and that he would not strip the engine because of that. Since my engine is built with larger pistons, he told me to replace the thermostat to a normal one (85-90c). The one that is in now opens at 63c. He thought the sound might go mostly away if the engine got up to normal temperatures. So I'll try that first ?

  • 5 months later...
On 28/06/2020 at 6:25 PM, Dil-Dog said:

Yeah man, good luck and take pics and get back to us 

Sorry for the really late answer, had a lot to do the latest months. But I guess I figured out what the problem was. Previous engine builder/company have done everything wrong... With the sound in the engine and it starting to fill fuel in the oil I was pretty sure that rings or pistons were worn. What I didn't expect after 40k km was this.

-Completely worn piston skirts

-Completely worn cylinders, and honing was done wrong. Honing marks were straight as an arrow in 80% of ALL the cylinders.

-Cylinders were so oval that if you turned the piston 90 or 180* it would not fit down in the cylinder.

All bearings looked great with no marks or wear, so that was not were the sound came from. New build starting early January when the parts arrive. Just got my new block finished at the machine shop, bored to 86.5mm and decked. Can't wait to get started and do it right this time!

 

20200724_193118.thumb.jpg.2f65829125f2948c19c46d30c84dde47.jpg20201010_210118.thumb.jpg.dd7494ef1fa7b27d23b3815e0d0d4511.jpg20201010_204328.thumb.jpg.123cc1ce01741eed4faebb707b6c5025.jpg20201010_205509.thumb.jpg.c5aa6baaffa9acbf65d42fe8387d34a6.jpg

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Yeah it is always worth testing and balancing actuators out of the box, just set the pressure regulator on a compressor very low (eg 5 psi) and increase it slowly to see when they both move.....unfortunately while you may be able to adjust the length of the actuator rod to minimise any difference, the actual pressure they move from is not adjustable so you need a well matched pair. And yes, the VCAM is probably contributing; the earlier in the rev range they come on boost and the slower the revs build (I think your demo was in 5th), the more you notice it.  Driving at WOT through 1st, 2nd, 3rd etc you will probably never hear it as any shuffling starts and is over super quickly
    • oh they were with that motor, you need to remove the engine to change the spark plugs (don't have to, but it does make it easier)
    • I certainly fall into the annoyed camp, but glad to hear that if it's happening at low boost then I'm not likely going to blow a turbo and end up with metal shards in my oil. Just feels like it prevents me from really driving it without hesitation and "peak" performance. Wonder if it's the VCAM, it did an impressive job of shifting the torque curve and faster spool, but maybe now it's "too fast" and there's too much air for how open the throttle is.  Based on some other threads, will also do some reading on synchronizing the actuators. They are the default actuators that come on the Garrett's and I would think they would be set the same coming from the factory, but if the turbos don't actually work exactly the same way at the same time as previously mentioned, it would be worth making sure the actuators are actuating together properly
    • I went down this rabbit hole before, ended up sourcing a motor from the UK (I'm in Japan) which also didn't function correctly. With the original motor, I disassembled it and reassembled it and it works somewhat, sometimes. What I could deduce from all my screwing around is that there is calibration of the gears on the inside of the motor and two ramps on the main gear which activate switches that operate the motor and move the sunroof either to retract into the roof or tilt. Where I got stuck was that, it seemed in my case that one or both of the switches that are activated by the ramp on the gear did not always activate and thus the motor did not move, causing it to sometimes not retract or tilt (apologies, I've forgotten which way it didn't work.).  Of course this part is discontinued at Nissan now, it's the same part in the S15 but no other models. I also contacted the manufacturer of the component for schematics - forgot the name, they're based in Gifu - but they declined to share the information due to being bound by an NDA, sadly. Looking through my pictures now, it seems I last had a crack at this in 2022. See, I so kindly wrote "open" and "close" next to the switches. If you figure it out, please do tell me. Those little switches, with the red buttons may need to be replaced.
×
×
  • Create New...